Superadiabatic combustion generation of reducing atmosphere for metal heat treatment

ABSTRACT

A system useful for superadiabatic combustion generation of a reducing atmosphere for metal heat treatment includes a superadiabatic reactor which supplies a reducing atmosphere to a metal heat treatment apparatus.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to the generation of a reducingatmosphere for heat treatment of metals, and more particularly togenerating a reducing atmosphere for heat treatment of metals fromsuperadiabatic combustion.

[0003] 2. Brief Description of the Related Art

[0004] Heat treatment of metals has been utilized to improve theproperties of metals. For example, U.S. Pat. Nos. 5,284,526, 5,298,090,and 5,417,774, all issued to Garg et al., describe processes forannealing metals in which nitrogen and residual oxygen are passedthrough a platinum-group catalyst reactor to convert the oxygen towater, and then passing this reaction product along with a hydrocarboninto the heating zone of a continuous furnace. According to Garg, thewater is converted to carbon dioxide and hydrogen by water gas shiftreaction, and a reducing atmosphere is produced for the heat treatmentof metal in the furnace.

[0005] Such prior processes suffer from several disadvantages. Therequirement for a catalyst in order for the reaction to proceed addsadditional costs to the process and apparatus. Furthermore, for manyprior processes, the reaction gases must be heated, which furthercomplicates the process and makes the overall process less efficient andsignificantly more costly. These prior processes are generally concernedwith combustion in a fuel-lean reaction.

[0006] Metal heat treatment in a controlled atmosphere has previouslybeen described. See, for example, U.S. Pat. Nos. 4,992,113, 5,057,164,5,069,728, 5,207,839, and 5,242,509, each of which is incorporated inits entirety herein by reference.

SUMMARY OF THE INVENTION

[0007] In accordance with a first exemplary embodiment in accordancewith the present invention, a process of heat treating metal comprisesthe steps of superadiabatically reacting a hydrocarbon with oxygen toproduce hydrogen, and exposing the metal to the hydrogen.

[0008] In accordance with a second exemplary embodiment in accordancewith the present invention, a system useful for heat treating metal witha reducing atmosphere comprises a superadiabatic reactor having aproduct gas outlet, and a metal heat treatment apparatus having an inletin fluid communication with said reactor gas outlet.

[0009] Still other objects, features, and attendant advantages of thepresent invention will become apparent to those skilled in the art froma reading of the following detailed description of embodimentsconstructed in accordance therewith, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The invention of the present application will now be described inmore detail with reference to preferred embodiments of the apparatus andmethod, given only by way of example, and with reference to theaccompanying drawings, in which:

[0011]FIG. 1 diagrammically illustrates a system in accordance with thepresent invention;

[0012]FIG. 2 schematically illustrates a first exemplary embodiment of asuperadiabatic reactor usable in the system of FIG. 1;

[0013]FIG. 3 schematically illustrates a second exemplary embodiment ofa superadiabatic reactor usable in the system of FIG. 1;

[0014]FIG. 4 illustrates a graph of a temperature profile of a portionof the reactor of FIG. 3 achievable in accordance with the presentinvention;

[0015]FIG. 5 illustrates a third exemplary embodiment of asuperadiabatic reactor usable in the system of FIG. 1; and

[0016]FIG. 6 illustrates a chart of the product distribution for methaneconversion as a fractional percent, achievable in accordance with thepresent invention, for two feed flow rates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Referring to the drawing figures, like reference numeralsdesignate identical or corresponding elements throughout the severalfigures.

[0018] The present invention relates generally to the reaction of anoxidant, preferably oxygen, by introducing hydrocarbon gases, e.g., CH₄,which produces a reducing atmosphere for metal heat treatment:

O₂+2CH₄→4H₂+2CO

[0019] The reaction of a hydrocarbon fuel and oxygen has, in the priorart processes, been catalyzed and performed as a fuel-lean reaction athigh temperatures, involving the further application of continuousexternal heating supplied to the reaction chamber. The presentinvention, in contrast, eliminates the need for both a catalyst andcontinuous external heating, and is preferably conducted fuel-rich.Thus, as in the patents to Garg, above, the fuel-lean reaction evolvescarbon dioxide and water, while the fuel-rich reaction preferable in thepresent invention evolves carbon monoxide and (diatomic) hydrogen gasuseful as a reducing atmosphere for metal heat treatment.

[0020] By using superadiabatic combustion, also termed excess enthalpycombustion, both the continuous external heating and the catalyst of theprior art can be eliminated from the reaction chamber. In general terms,once ignition starts with the assistance of a startup heater, thestartup heater can be turned off and the temperature of thesuperadiabatic reactor of the present invention can be maintained atcombustion temperature.

[0021] Excess enthalpy (superadiabatic) combustion has been wellexamined in the literature. See, e.g., Weinberg, F., SuperadiabaticCombustion and Its Applications, in International School-Seminar,Contributed Papers, Minsk, Belarus, Aug. 28-Sep. 1, 1995, pp. 1-20,which reviews superadiabatic combustion principles and describes severalexemplary superadiabatic reactors. In general, the effect ofsuperadiabatic combustion occurs when a mixture of gaseous fuel and anoxidizer, which mixture has an overall low caloric value (i.e., lowadiabatic temperature) passes through an inert, solid, porous bodyhaving a high heat capacity. The intense heat exchange during oxidationof the fuel between the combustion gases and the porous body permitsaccumulation of energy from combustion in the body. Thus, the flametemperature achieved can be much higher than the adiabatic temperatureof the feed fuel mixture, because of the effective heat transferfeedback to the feed gases from the porous body. Although superadiabaticreactors have been proposed for use in some applications, the presentinvention for the first time combines the advantages of excess enthalpycombustion with a metal heat treatment process and apparatus.

[0022]FIG. 1 illustrates a system in accordance with the presentinvention, which includes a superadiabatic reactor 100 connected to anexemplary metal treatment apparatus 10 by a flow pathway 102. Metal tobe treated (not illustrated) is exposed in apparatus 10 to a treatmentgas supplied to the apparatus from reactor 100. The details of apparatus10 will be readily understood by one of ordinary skill in the art, andmay be any of numerous metal treatment apparatus which have been or willbe proposed, including those described in the aforementioned U.S. Pat.Nos. 4,992,113, 5,057,164, 5,069,728, 5,207,839, and 5,242,509,including high temperature furnaces. Accordingly, additional details ofapparatus 10 are not included herein.

[0023]FIG. 2 schematically illustrates a first exemplary embodiment of asuperadiabatic reactor usable as reactor 100 in the system of FIG. 1,reactor 104. Reactor 104 includes a reactor vessel 106, which ispreferably insulated so that heat transfer from the vessel iscontrolled, and preferably minimized. Vessel 106 includes an entrance108 which allows a feed gas or feed gas mixture to enter the vessel, andan exit 110 which allows a product gas or product gas mixture to exitthe vessel. Preferably, exit 110 is in fluid communication with pathway102, illustrated in FIG. 1.

[0024] Reactor 104 includes a porous solid medium 112 in vessel 106,formed of a high temperature refractory, ceramic (e.g., aluminum oxide),or similar high temperature material, and includes gas pathways (notillustrated) therethrough, so that gas may readily flow through themedium 112. Reactor 104 also includes a start-up heater 114,simplistically illustrated in FIG. 2 as a box, which can be activated toheat up medium 112 to a temperature sufficient to ignite feed gasflowing through vessel 108. As will be described in greater detailbelow, heater 114 can be deactivated or turned off once a superadiabaticreactor in accordance with the present invention is generating enoughenergy to maintain its own process, which can result in significantenergy savings over prior systems which require continuous heating toproduce metal treatment gas, as discussed elsewhere herein. In order tomonitor reactor 104, as well as other embodiments of reactor 100described herein, the reactor is provided with temperature probes orthermocouples (not illustrated) mounted in heat transfer communicationwith the reactor, which provide data signals indicative of thetemperature of the reactor. This temperature signal data can be used inan appropriate feedback control scheme, implemented in a manner wellknow to those skilled in the art, to control the temperature of thereactor and the combustion therein.

[0025]FIG. 2 illustrates an exemplary feed gas mixture entering entrance108, the mixture including nitrogen, oxygen, and a hydrocarbon.Preferably, the feed gas is fuel-rich, i.e., the hydrocarbon fuel ispresent in the feed gas in an amount greater than the stoichiometricamount for the combustion reaction for that hydrocarbon. Hydrocarbonsuseful in the present invention include, but are not limited to,methane, hexane, propane, butane, and methanol; methane is used hereinas an exemplary hydrocarbon from which a product gas, hydrogen, isproduced. As will be readily appreciated by one of ordinary skill in theart, the stoichiometric ratio for oxidizing (combusting) methane is 2,as evident from the above balanced equation. Thus, fuel-rich combustionof methane, for example, involves a CH₄/O₂ ratio greater than 2, whilefuel-lean combustion of methane involves a ratio less than 2.

[0026] As seen from FIG. 2, the feed gas mixture enters vessel 106, andpasses through medium 112. As startup heater 114 has already heated upmedium 112 to a temperature sufficient to at least partially oxidize themethane, the methane is oxidized, producing carbon monoxide and hydrogengas. The heat energy released by this exothermic reaction heats themedium 112, which heats incoming feed gas by radiation heat transfer,conduction heat transfer, or both. As the incoming feed gas is thereforepreheated by energy from the reaction downstream of it, a reaction heatfeedback 116 is established. Further details of excess enthalpy orsuperadiabatic combustion are well reviewed in Weinberg, above, and willnot be further detailed herein.

[0027]FIG. 3 schematically illustrates a second exemplary embodiment ofa superadiabatic reactor usable as reactor 100 in the system of FIG. 1,reactor 130. Reactor 130 includes a feed inlet 132, a product outlet134, and an insulated porous solid medium 136, similar to medium 112.Medium 136 includes a start-up heater (not illustrated). First andsecond two-way valves 138, 140 are connected by fluid pathways 150, 152,to ports 158, 160, respectively, of medium 136. Reactor 130 includes afeed inlet flow path which includes an upper branch 142 and a lowerbranch 144. Upper branch 142 fluidly connects feed inlet 132 with valve138, and lower branch 144 fluidly connects the feed inlet with valve140. Reactor 130 also includes a product outlet flow path which includesan upper branch 146 and a lower branch 148. Upper branch 146 fluidlyconnects product outlet 134 with valve 138, and lower branch 148 fluidlyconnects the product outlet with valve 140.

[0028] Valves 138, 140 can be switched between two positions each, whichtogether determine the direction of flow of gas through reactor 130. Ina first set of positions of valves 138, 140, a first flow path “A” isestablished. Feed gas is prevented from flowing along lower inlet branch144 by valve 140 and is allowed to flow through upper inlet branch 142to valve 138. Valve 138 directs the flow of feed gas along pathway 150into port 158 of medium 136. As the feed gas passes through medium 136,it is at least partially combusted to form a product gas, e.g.,hydrogen, and the reaction products exit the medium at port 160. Theproduct gas passes along pathway 152 and is directed by valve 140 alonglower branch 148 to product outlet 134. When set in the first position,valve 138 prevents product gas from entering pathway 150 and reenteringmedium 136.

[0029] Valves 138, 140 can be positioned to establish a second flow path“B”, which is, in one sense, opposite flow path “A”. Feed gas isprevented from flowing along upper inlet branch 142 by valve 138 and isallowed to flow through lower inlet branch 144 to valve 140. Valve 140directs the flow of feed gas along pathway 152 into port 160 of medium136. As the feed gas passes through medium 136, it is at least partiallycombusted to form a product gas, e.g., hydrogen, and the reactionproducts exit the medium at port 158. The product gas passes alongpathway 150 and is directed by valve 138 along upper branch 146 toproduct outlet 134. When set in the second position, valve 140 preventsproduct gas from entering pathway 152 and reentering medium 136.

[0030] Thus, when valves 138, 140 are set to establish path “A”, gasflows through medium 136 in the direction indicated by arrow 154, andthe high temperature volume of medium 136, e.g., the flame front fromcombustion of methane, expands or moves in the direction indicated byarrow 156. Similarly, when valves 138, 140 are set to establish path“B”, gas flows through medium 136 in the direction indicated by arrow156, and the high temperature volume of medium 136, e.g., the flamefront from the combustion of methane, expands or moves in the directionindicated by arrow 154. To maintain the flame front within the medium136, and therefore to prevent the flame from flashing back into the feedgas supply, and also to trap heat in the porous medium, valves 138, 140are switched between the first and second sets of positions, whichreverses the flow as described above. By reversing the flow directionsthrough medium 136, the flame front can be caused to move back and forthwithin the medium to maintain the medium at a very high temperature,thus allowing superadiabatic combustion to continuously occur.

[0031]FIG. 4 illustrates a graph of a temperature profile medium 136achievable in accordance with the present invention. As illustrated inFIG. 4, the average temperature of the medium at the inlet (leftendpoint) and outlet (right endpoint) can be maintained around 30° C.,while average temperatures within the porous solid medium can reach 800°C. by timing the flow reversal to occur when the heat wave nearlyreaches the ports 158, 160. The excess enthalpy and heat transfer fromcombustion at this temperature is sufficient to maintain combustion inthe porous medium without the need for an additional, external heater orcatalyst.

[0032]FIG. 5 illustrates a third exemplary embodiment of asuperadiabatic reactor usable for reactor 100 in the system of FIG. 1,reactor 180. Reactor 180 is a recuperative-type reactor. Reactor 180includes a bed of a porous solid medium 182 in which excess enthalpycombustion of the hydrocarbon fuel occurs. As illustrated in FIG. 5,porous bed 182 has an exposed top surface 190, and a feed tube 186extends into the bed through the top surface. Porous bed 182 isotherwise closed off and, as in the other embodiments herein, isinsulated and provided with a start-up heater (not illustrated). Thus,feed gas 184 is supplied through feed tube 186 into porous bed 182 whereit reacts. Product gas 188 leaves the porous bed and flows around thefeed tube. The portions of the porous bed which surround the feed tube,as well as the hot product gas, transfer heat to the feed tube and thefeed gas therein, thus assisting in maintaining excess enthalpycombustion in reactor 180.

[0033] Reactor 180 can optionally further be provided with a carrier gastube 192 (illustrated in phantom) inside feed tube 186, which can supplya non-reactive carrier gas into medium 182. The further provision ofcarrier gas tube 192 permits the total mass flow rate into reactor 180to be controlled by controlling the mass or volume flow rate of thecarrier gas flowing through the carrier gas tube, which in turn controlsthe temperature of the reactor.

[0034]FIG. 6 illustrates a chart of the product distribution for methaneconversion, as a fractional percent, achievable with the reactor of FIG.5, for two feed gas flow rates. For both flow rates, the ratio ofhydrocarbon (methane) to oxygen was 1.40 (fuel lean). As demonstrated bythe data represented in FIG. 6, the relatively slow mass flow rate (0.17g/sec) produced a greater fractional percent of hydrogen than the fastmass flow rate (0.20 g/sec), which can be attributed to a highercombustion temperature because of the longer residence time of thereaction gas in the reactor.

[0035] Each of the aforementioned U.S. patents and literature referencesis incorporated by reference herein in its entirety.

[0036] While the invention has been described in detail with referenceto preferred embodiments thereof, it will be apparent to one skilled inthe art that various changes can be made, and equivalents employed,without departing from the scope of the invention.

What is claimed is:
 1. A process of heat treating metal, comprising thesteps of: superadiabatically reacting a hydrocarbon with oxygen toproduce hydrogen; and exposing said metal to said hydrogen.
 2. A processin accordance with claim 1, wherein said reacting step further comprisesreacting in a porous solid medium.
 3. A process in accordance with claim1, further comprising preheating said porous medium with a heaterelement prior to said reacting step.
 4. A process in accordance withclaim 3, further comprising terminating said preheating step at theearliest at the commencement of said reacting step.
 5. A process inaccordance with claim 1, further comprising the steps: providing areactor including a porous solid medium having a first end and a secondend, a first port at said first end and a second port at said secondend, a first two-way valve in fluid communication with said first portand a second two-way valve in fluid communication with said second port,a feed flow path having an inlet, a first branch, and a second branch, aproduct flow path having an outlet, a first branch, and a second branch,said feed flow path first branch fluidly communicating said feed inletwith said first two-way valve, said feed flow path second branch fluidlycommunicating said feed inlet with said second two-way valve, saidproduct flow path first branch fluidly communicating said product outletwith said first two-way valve, and said product flow path second branchfluidly communicating said product outlet with said second two-wayvalve; and flowing said hydrocarbon through said feed flow path intosaid porous medium.
 6. A process in accordance with claim 5, whereinsaid flowing step further comprises flowing said hydrocarbon seriallythrough said feed flow path first branch, said first two-way valve, saidfirst port, said porous solid medium, said second port, said secondtwo-way valve, said product flow path second branch, and said productoutlet.
 7. A process in accordance with claim 6, wherein said flowingstep further comprises actuating said first and second two-way valveswhen a flame front in said porous solid medium is adjacent said firstport so that said flowing step comprises flowing said hydrocarbonserially through said feed flow path second branch, said second two-wayvalve, said second port, said porous solid medium, said first port, saidfirst two-way valve, said product flow path first branch, and saidproduct outlet.
 8. A process in accordance with claim 1, furthercomprising the steps: providing a reactor including a porous solidmedium having a first end and a closed second end, a port at said firstend, and a feed tube extending into said porous solid medium throughsaid first end; flowing said hydrocarbon through said feed tube intosaid porous solid medium; and flowing said hydrogen out of said poroussolid medium and around said feed tube.
 9. A process in accordance withclaim 1, wherein said reacting step comprises reacting a ratio ofhydrocarbon to oxygen in a ratio of hydrocarbon to oxygen greater than astoichiometric ratio.
 10. A process in accordance with claim 1, whereinsaid hydrocarbon is selected from the group consisting of methane,hexane, propane, butane, and methanol.
 11. A process in accordance withclaim 1, wherein said reacting step comprises reacting said hydrocarbonin the absence of a catalyst.
 12. A system useful for heat treatingmetal with a reducing atmosphere, comprising: a superadiabatic reactorhaving a product gas outlet; and a metal heat treatment apparatus havingan inlet in fluid communication with said reactor gas outlet.
 13. Asystem in accordance with claim 12, wherein said superadiabatic reactorcomprises a porous solid medium.
 14. A system in accordance with claim13, wherein said porous solid medium includes a first end and a secondend, a first port at said first end and a second port at said secondend, a first two-way valve in fluid communication with said first portand a second two-way valve in fluid communication with said second port,a feed flow path having an inlet, a first branch, and a second branch, aproduct flow path having an outlet, a first branch, and a second branch,said feed flow path first branch fluidly communicating said feed inletwith said first two-way valve, said feed flow path second branch fluidlycommunicating said feed inlet with said second two-way valve, saidproduct flow path first branch fluidly communicating said product outletwith said first two-way valve, and said product flow path second branchfluidly communicating said product outlet with said second two-wayvalve.
 15. A system in accordance with claim 13, wherein said poroussolid medium includes a first end and a closed second end, a port atsaid first end, and a feed tube extending into said porous solid mediumthrough said first end.
 16. A system in accordance with claim 12,wherein said superadiabatic reactor comprises a heater.